Remote indication apparatus



Sept. 27, 193%. E, M, ALLEN REMOTE INDICATION APPARATUS 2 Sheets-Sheet 1 Filed Feb. 26, 1958 wd wi Qgrv.

lNV N TOR Ear .Aller). BY

' HIS ATTORNEY SNSQ wQb Sept. 27,1938. E. M. ALLEN REMOTE INDICATION APPARATUS 2 Sheets-Sheet 2 Filed Feb. 26, 1958 N MQ SNSQ BENK INVENTOR HIS ATTORN EY Patented Sept. 27, 1938 UNITED STATES REMOTE INDICATION APPARATUS Earl M. Allen, Swissvale, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application February 26, 1938, Serial No. 192,838

10 Claims.

My invention relates to remote indication apparatus, and more particularly to apparatus for continuously indicating at a remote point, such, for example, as a dispatchers office, the occupancy of railway track sections.

A feature of my invention is the provision of novel and improved indication apparatus wherewith two continuous indications can be effected by direct current over a single two-wire line circuit. Another feature of the invention is the provision of indication apparatus operative to establish in response to a first control impulse of a predetermined duration an indication which is continued after the impulse, and to cancel the indication in response to a second and similar control impulse. Other features and advantages of my invention will appear as the specification progresses.

I shall describe two forms of apparatus embodying my invention, and shall then point out 2 In each of the two views, like reference characters designate similar parts.

In Fig. l, the lineargraph shown at the upper right-hand portion of the drawing designates a stretch of single track railway including a track 30 switch and wayside signals for governing traffic over the switch. The track is formed in the usual manner into track sections. In the instant case, two approach track sections LDT and LT are provided to the left of the track switch SW and two approach track sections EDT and RT 0 are provided to the right of the switch. Moreover, the usual detector track section IT is provided at the switch location. Each of these track sections is provided with a track circuit including a track relay which is identified by the reference character R plus a prefix corresponding to the section, the relationship of a track relay with its section being indicated by a dash line. The track relay for the detector section IT is not shown, since it is not required to describe my present invention. It will be understood, of course, that my invention is not limited to the track layout shown in Fig. 1. For example, only one approach section on each side of the track switch may be used, and furthermore, the two sections may be adjacent to each other. Moreover, it will be understood that my invention is not limited in its use to railway track sections, and this one use of the invention will serve to illustrate the 55 many places where the invention may be used.

The wayside signals associated with the track switch SW are shown conventionally and may be of any standard type governed by any of the'wellknown systems of control circuits. These signal control circuits are not shown for the sake of simplicity, since they form no part of my present invention, and a description thereof is not required for an understanding of theinvention.

A field station FS, preferably located adjacent the track switch SW, is connected with a remote 10 ofiice station, such as a dispatchers office DO, by a two-wire line circuit including a line wire LW and a common line wire CL. The field station FS is provided with a source of direct current, such as a battery 25, having a positive ter- 15 minal B, a negative terminal N and a central terminal C, the terminal C being connected with the common line wire CL.

Two approach relays LAR and RAR are located I at the field station FS, the relay LAR being con- 20 trolled over a simple circuit serially including front contacts 20 and 2| of track relaysLDTR and LTR, respectively; and the relay RAR being controlled over a simple circuit serially including front contacts 22 and 23 of track relays RDTR and R'I'R, respectively. It follows that, as long as no train is approaching the track switch SW and the approach track sections are unoccupied, the approach relays LAR and RAR are picked up, but that a train occupying either or both sections LDT and LT deenergizes relay LAR and a train occupying either or both sections EDT and RT deenergizes the relay RAR.

A direct current polar relay 8P is controlled 7 by the approach relays LAR and RAR, the relay 8Pbeing preferably of a type that its polar armature 30 remains in the position to which it was last moved when the winding 24 of the relay is deenergized. As viewed in Fig. 1, the lefthand terminal of winding 24 of relay SP is connected with the negative terminal N of the battery 25 over afront contact 26 of relay LAR, and with the positive terminal B of battery '25 over a back contact 21 of relay LAR. The righthand terminal of winding 24 is connected with the N terminal of battery 25 over a front contact 28 of relay RAR, and is connected to the B terminal of battery 25 over a back contact 29 of relay RAR. Consequently, the winding 24 of relay 8P is deenergized when both approach relays LAR and RAR are picked up, and also when both of these relays are released. With relay LAR picked up, closing front contact 26, .and relay RAR released, closing back contact 29, the winding 24 of relay 8P is energized with current which I shall term 55 the relay is moved to the left-hand position to engage a normal polar contact 54. With relay RAR picked up, closing front contact 28, and relay LAR released, closing back contact 21, the winding 24 is energized wth current whch I shall term reverse polarity, and the polar armature 3|] is moved to the right-hand position to engage a reverse polar contact 50. I

The polar relay BP and the approach relays LAR and RAR govern a series of circuit connections for supplying current from the battery 25 to the line circuit. With normal polar contact 30-54 of relay 8P closed, a connection is completed from the N battery terminal when relay LAR is picked up, closing front contact 58, and another connection from the B terminal of the battery is completed when relay LAR is released, closing back contact I03. Again, when the re verse polar contact 305ll is: closed, a connection from the N battery terminal is completed over back contact 55 of relay RAR, and a connection is completed from battery terminal B over front contact of relay RAR.

Three relays 5L, 6L and IL are introduced in the field station apparatus for at times controlling the above cited connections between the battery 25 and the line circuit. The relays BL and IL are slow releasing in character, and the relay 5L is of the ordinary acting type. The release periods for relays 6L and IL are preferably alike and are made of a duration predetermined with respect to the release periods of certain relays of the office station apparatus, to be described later. The relay 6L is energized over a simple circuit including back contact 3| of approach relay LAR, and relay IL is energized over back contact 32 of the approach relay RAR. The relay 5L is provided with an energizing circuit including three branch paths one path of which serially comprises front contacts 33 and 34 of the approach relays LAR and RAR, respectively; a second branch path comprises front contact 35 of relay LAR and a front contact 36 of relay 6L; and a third path comprises front contact 31 of relay RAR, and a front contact 38 of relay IL. A

back contact 51 of relay 5L is interposed in the connection to the line wire LW, as will be readily understood by an inspection of Fig. 1. The'manner whereby the relays 5L, 6L and IL govern the connections tothe line circuit will appear when the operation of the apparatus of Fig. 1 is described. Y

At the ofiice station DO, a neutral relay ID and a polar relay 2P are governed by the line circuit, the winding 39 of relay ID having its opposite terminals connected directly with the line wires LW and CL, and the winding 4|] of relay 2P having one terminal connected directly with the common line wire CL and its other terminal connected with the wire LW over a front contact 4| of relay ID. Thus, when direct current is supplied to the line circuit in a manner to shortly appean'the relays ID and 2P are energized, the relay ID being picked up irrespective of the polarity of the line circuit current and the polar relay 2P being energized to move its polar armature 42 to the left-hand position to engage a normal' polar contact 53 when the line circuit current is of normal polarity and to operate armature 42 to the right-hand position to engage a reverse polar contact 55' when the line circuit current is of reverse polarity.

normal polarity, and the'polar armature 30 of I each provided with a stick circuit. Relay 3K or 4K when once selected by relays ID and 2P is retained energized by its stick circuit when the polarity of .the line circuit current is reversed, but is released when the line circuit current is dis- 1 continue-d'for an interval greater than the slow release period of the relay. The stick circuit for 'rel'ay'3K comprises a front contact 44 of relay ID and its own front contact 45, and the stick circuit for relay 4K comprises a front contact 46 of relay ID and its own front contact 41.

Two indicators LI and RI are included in the office station apparatus for indicating the occupancy of the approach track sections associated with the switch SW, the indicator LI being associated with the approach track sections LDT and LT and the indicator RI being associated with the track'sections RDT and RT. The type of indicator is immaterial and, as here shown, they are visual indicators in the form of electric lamps. The indicator LI is illuminated over front contact 48 of indication relay 3K, and the indicator RI is illuminated over front contact 49 of relay 4K.

In describing the operation of the apparatus of Fig. l, I shall assume at the start that the track sections are all unoccupied so that the relays at both the field station and the office station are in the position illustrated in Fig. 1 and the indicators LI and RI are dark. I shall next assume that a train of sufficient length to extend over sections LT, IT and RT approaches the track switch SW from the left. This train, upon entering section LDT and shunting track 'relay' LDTR to open front contact 20, deenergizes the approach relay LAR and that relay is released. With relay LAR released, opening front contact 33, the relay 5L is deenergized and released, closing its back contact 51. With back contact 2! of relay LAR closed, the polar relay 8P is energized with current of reverse polarity, operating its polar armature 30 to close the reverse polar contact 3U-50 Current of normal polarity is now supplied to the line circuit from terminal B of battery over front contact SI of relay RAR, reverse polar contact 3ll--50 of relay BP and back contact 51 of relay 5L. This line circuit current of normal polarity is effective to first energize relay ID at the office station, and then to energize polar relay 2P when relay ID is picked up, closing its front contact 4|. With relay 2P energized with current of normal polarity to close its normal polar contact 42-53, the indication relay 3K is selected over its pickup circuit. Relay 3K on picking up completes its stick circuit and causes the indicator LI to become illuminated to indicate the occupancy of the track section LDT. It should be observed that when the approach relay LAR is released in response to the train entering section LDT the relay BL is energized over back contact 3| ofrelay LAR, but the operation of relay 6L at this time performs no function except to prepare the circuit for relay 5L at'front contact 36 of relay 6L.

f When the train advances to the right through section LDT and enters the track section LT,

the approach relay LAR remains deenergizedso that the line circuit is still supplied with current of normal polarity and the lamp LI continues to be illuminated to indicate the presence of the train in the sections LDT and LT.

When the train advances through section IT and the head end of the train enters section RT, the rear of the train still occupying section LT, the track relay RTR is shunted and released to open the circuit for the approach relay RAR, and relay RAR is deenergized and-released, the approach relay LAR still remaining deenergized due to the presence of the train in section LT. With both approach relays LAR and RAR released, the polar relay BP is deenergized, its polar armature remaining in engagement with the reverse polar contact 5|]. Current of reverse polarity is now supplied to the line circuit, current flowing from terminal C of battery 25 over line wire CL, windings 39 and 40 of. relays ID and 2P in multiple, line wire LW, back contact 51, reverse polar contact 30-50, back contact 56 of relay RAR and negative terminal N of battery 25. This reversal in the polarity of the line circuit current reverses the energization of relays ID and 2P, causing relay 2P to operate its armature 42 to engage the reverse polar contact 55, and causing relay ID to be momentarily released during the period the magnetic flux of the relay is passing through zero. With relay ID again picked up, closing its front contact 43, the indication relay 4K is selected, and relay 4K on picking up, closing front contact 49, completes the circuit for lamp RI, so that lamp RI is now illuminated to indicate the presence of the train in section RT. Since the indication relay 3K is slow releasing in character, it does not release during the short interval the relay ID is released in response to the reversal of the polarity of the line circuit current, and hence relay 3K is retained energized over its stick circuit. It follows that because of, the rapidity in which the reversal of the polarity of the line circuit' current is effected the indication relay 3K remains picked up and the lamp LI remains illuminated to indicate the presence of the train in section LT. It is to be observed that when the approach relay RAR is released, closing back contact 32, the relay IL is energized and picked up but the operation of relay IL at thistime performs no useful function.

The next operation step is effected when the train moves on to the right and the rear of the train vacates the track section LT so that the approach relay LAR is reenergized and picked up. With relay LAR picked up, opening back contact 3|, the relay BL is deenergized and released at the end of its slow release period. During the release period of relay 6L, the relay 5L is provided with a circuit including front contacts 35 and. 36, and consequently relay 5L is picked up, opening the line circuit at back contact 51 during the release period of relay 6L. With relay 6L released, the relay 5L is immediately released to reclose the line circuit.

The polar relay 8P is now energized by current of normal polarity over back contact 29 of relay RAR and front contact 26 of relay LAR, and its normal polar contact 30-54 is closed. Thus, when the connection to the line circuit is reclosedat back contact 5I, curre nt of reverse polarity is again supplied to the line circuit, thecircuit being substantially the same as previously traced except it now includes the connectioncompleted at normal polar'contact 30-54 of relay BP and front contact 58 of relay LAR.

During the interval the line circuit is without current, the relays ID and 2P are deenergized, the relay ID being released but the polar relay 2P remaining with its reverse polar contact 42-55 closed. As set forth hereinbefore, the

polarity is again supplied thereto so that the relays ID and 2P are reenergized, the indication relay 4K is again selected'but the relay 3K remains released, since both its pick-up and stick circuits are now open. Consequently, the lamp LI is now extinguished to indicate that the train has vacated section LT, but the lamp RI is still illuminated to indicate the presence of the train in the section RT. That is, when the section LT is vacated while section RT is occupied, the polarity of the line circuit current remains the same, but the line circuit current is discontinued for an interval great enough to cause the release of the indication relay 3K and the extinguishing of the lamp LI.

When the train moves on to the right through section RDT and vacates section RDT, approach relay RAR is picked up so that relay 5L is reenergized over front contacts 33 and 34 and the line circuit current is discontinued, with the result that relay 4K is released and the lamp RI is extinguished.

If the train is short, the operation described above is substantially the same except both indicators LI and RI may be dark during the interval IT. It will be understood, of .course, that any remote control systems used for governing the track switch SW and the signals related thereto would ordinarily include an indication for the detector track section IT.

The operation of the apparatus of Fig.- 1 for a train moving from right to left is similar to that just described for a train moving from left, to right, and the description for the operation for a train moving from right to left need not be described except to point out that. when the train occupies the sections RDT and RT and relay RAR is deenergized, the polar relay 8P is energized with current of normal polarity, current ofreverse polarity is supplied to the line circuit over front contact 58 of relay LAR and normal polar contact 30-54 of relay BF, and indication relay 4K is selected to illuminate the indicator RI. Also, the relay IL is energized and picked up. to prepare the circuit for relay 5L. When the head end of the train enters section LT and the rear end of the train still occupies section RT, the polar relay 8P is deenergized and current ,of normal polarity is supplied to the line. circuit over back contactI03'of relay LAR and normal polar contact 30-54 of relay 8P. The polarity Relay 3K is now also energized when relay-2Pis operated to its normal position-so that lamp 'LI is illuminated' along with lamp RI to indicate the presence of the train in both-approach sections LT and RT. When' the rear of the-train vacates section RT, the relay 5L is picked up-over front contacts 37' and 38 during the slowrelease period of relay IL;- and then current of norma'l polarity is again supplied to the line circuit when relay-5L is'released to reclose the line circuit at back contact 5! of relay 5L. The :duration during which the line circuit current is discontinued (release period of relay 'IL) is long enough to permit indication relay 4K to release, with the result that lamp R! is extinguished to indicate that-ithe train has vacated the section RT. 'In the' 'event the train-moving from right to'left moves to the siding, the approach relay RAR is reenergized and picked-up to open the line circuit and the lamp RI is extinguished in response to the train vacatingthe section RT. I

In'Fig. 2, the track layout, field station, ofiice station and line circuit between the twostations are the same as in Fig. 1. a

The approach relays LAS and RAS of Fig. 2 are slow releasing in character and each is provided with a pick-up circuit and a stick circuit. The pick-up circuit for' relay LAS serially ineludes front contact 59 of track-relay'LDTR, front contact 60 of track relay LTR and back contact 6| of a relay- I 3L to be referred to later. The stick circuit for relay LAS is completed at front contact 62 of relay I3L and its own front contact 63. In a similar manner, the pick-up circuit for relay RAS comprises front contacts 64 and 65 of track relays RDTR. and RTR, respectively, and back contact 66 of a relay ML to be shortly described; and its stick circuit comprises front contact 61 of relay MLand its own front contact 68. a I I A pair of slow releasing relays 9L and IIIL are associated with the approach relay RAS, the relay 9L being controlled over front contact 69 of relay RAS and the relay IBL being energized over back contact III of relayRAS. In like manner, a pair of slow releasing relays IIL and I2L are controlled by the approach relay LAS, the circuit for relay IIL including front contact -II o'frela'y LAS and the circuit for relay 42L being completed at back contact 12 of relay-LAS: The approach relay RAS and its associated relays 9L- and 'IBL govern a quick acting relay BL, and the approach relay LAS and its associatedrelays I IL and I2L govern a second quick acting relay ML. The energizing circuit for relay I3L comprises twobranch paths one of which is formed over front contacts and I6 of the respective relays RAS and: IOL, and the other branch path is formed over back contact TI- of relay RAS and front contact I8 of relay 9L. Similarly, the energizing circuit for relay ML comprises two branch paths one of which is formed over front contacts I9 and 80 ofthe respective relays LAS and I2L, and the other path of which is formed over back contact 8| of relay LAS and front contact 82-of relay IIL.

The relays I3L and ML are introduced in the field station apparatus of Fig. 2 .for governing the connection of battery to the line circuit as well as for governing the circuits for the approach relays in a manner explained hereinbefore. The negative terminal N of battery 25 isconnected with line wire LW over front contact I3 of relay I3L, and the positive terminal B of battery 25 is connected with line wire'LW over front contact-"14 ofrelay ML. The period in which the relay I3L or ML is picked up to com- -plete=its connection to'the line circuit depends upon the slow release periods of the relays 9L and IBL in the case of relay ISL, and upon the 1 and 2P are connected with the linecirouit the 7 same as in Fig. 1, except the connection of winding "of relay 2P withth line wire LW does not include a front contact of relay ID. In this form of the invention, the relays ID and 2P selectively govern two quick acting relays 3D and 6D, the relay 3D being selected over front contact 83 of relay ID and the normal polar contact 84-89 of relay 2P, and the relay 6D being selected over front contact 83of relay ID and reverse polar contact 84-96 of relay 2P.

The relay 3D'in turn governs two slow releasing indication relays 4D and 5D, and the relay 6D in turn governs two slow releasing indication relays ID and 8D. The relays 5D and 8D are both normally energized, the circuit for relay 5D being completed over back contacts 85 and 86 of relays 3D and 4D, respectively; and the circuit for relay 8D being completed over back contacts 81 and 88- of the respective relays 6D and ID. The slow release periods for the relays 4D, 5D, IDand BD'arepreferably alike and are slightly shorter in duration than the slow release period predetermined for the field station relays 9L, IIJL, IIL and IZL.

To describe the operation of the apparatus of Fig. 2, I shall first assume that the track sections are unoccupied and the relays at both the field station and at'the office station are in their normal positions, that is,-the positions illustrated in the drawings. I shall next assume that a train of some length approaches the sections from the left. Entry of the train into section LDT, shunts trackrelay LDTR to'open front contact 59, and the approachrelay LAS is deenergized and releases at the end of its slow release period. The relay LAS, releasing to open front contact II, deenergizes relay IIL, which releases at the end Of'its slow release period. The closing of back contact 8| o-f'relay LAS, causes relay ML to be supplied'with current and picked up during the slow release period of relay IIL, relay ML being .deenergized and released when relay IIL is released. During this interval that relay ML is picked up, closing front contact M, current of normal polarity is supplied to the line circuit and the relay ID is picked up; closing front contact 83, and the, relay 2P is operated to close its normal polar contact 84-49 sothat relay 3D is energized and picked up. At the end of this impulse of line circuit current, the relay ID, and in turn relay 3D, are deenergized and released. During the interval relay 3D is picked up, the relay 4D is supplied with current over its pickup circuit including front contact 90 of relay 3D and front contact SI of relay 5D. The circuit for relay 5D being now open at back contacts 85 and 86, relay 5D is deenergized and releases prior to the termination of the line circuit current impulse, since, as pointed out hereinbefore, the release period-of relay 5D is less than the release period of relay IIL at the field station.

Thus, when relay 3D is released at the end of the line circuit current impulse, the relay 4D is retained energized over its stick circuit including back contact 92 of relay 5D, its own front con: tact 93 and back contact 85 of relay 3D. With relay 4D picked up, closing front contact 94, and relay 5D released, closing back-contact 95, the lamp LI is illuminated to indicate the presence of the train in the section LDT. Entry of the train into section LT to shunt track relay LTR retains the approach relay LAS deenergized .and no additional operation of the field station apparatus takes place, so that lamp LI continues to be illuminated. Thus, the occupancy of the sections LDT and LT is continuously indicated at the" office station in response to the impulse of current of normal polarity of a predetermined length supplied to the line circuit, and no line circuit energy subsequent to the termination of this im pulse is required. 7

Assuming the train after entering section LDT reverses its movement and backs to the left outof the section, an impulse of current of normal polarity is again supplied to the line circuit to cause the lamp LI to be extinguished. When approach relay LAS is picked up in response to the train backing out of the section LDT, the opening of back contact I2 causes the relay I2L to be deenergized and releasedat the end of its slow release period. The relay I4L is picked up over front contacts I9 and during the release .peri- 0d of relay I2L, and then relay I 4L is immediately released when the relay I2L is released. This impulse of current of normal polarity sup-. plied to the line circuit energizes relays ID and 2P, the same as before, so that relay 3D is selected and picked up to open the stick circuit of relay 4D at back contact 85. Since the release period of relay I2L isgreaterthan the release period of indication relay4D, the relay 4D is released prior to the termination of the impulse of line circuit current and the releaseof relay 3D. The indication relay 4D is not again picked up open at front contact 9| of relay 5D. Consequently, the relays 4D and 5D are returned to their normal positions and. the lamp LI is exting'uished. That is to say, a first impulse of line circuit current of normal polarity and of a predetermined duration causes lamp LI to be illuminated and a second impulse of line circuit current of the same polarity and duration is effective to extinguish the lamp LI.

Assuming the train instead of backing out of section LDT proceeds to the right through sections LT and IT into section RT the rear of the train still being in section LT, the track relay RTR is shunted and approach relay RAS is deenergized and released at the end of its slow re lease period in response to entry of the train into section RT. When relay RAS is released, the relay I3L is picked up over back contact 11 of relay RAS and front contact I8 of relay 9L, while relay BL is deenergized since its circuit is open at front contact 69 of relay RAS. Thus, relay I3L is picked up during the slow release period of relay 9L, and during theinterval relay I3L is picked up an impulse of current of reverse polarity is supplied to the line circuit. This impulse of current of reverse polarity causes relay ID to be picked up and relay 2P to be operated to close its reverse polarv contact 8496, and re- 1y at the end of the impulse of line circuit current. [The pickingup of relay 6D opens the circuit of relay 8D and since the release period of relay 8D is less than the release period of relay- 9L, the relay 8D is released'prior to the end of r the line circuit current impulse. The indication relay ID is energized first over its pick-up circuit including front contacts 9! and 98, and-is retained energized over its stick circuit including back contact 81 of relay 6D, its own front contact I00 and-back contact 99 of relay 8D. sub

current of reverse polarity supplied to the line circuit in response toentry of the train into sectionRT does not affect the relay 3D, and hence the indication relay 4D is retainedi energized over .itsstick circuit and the lamp LI continues to be illuminated. Both lamps LI and RI are thus displayed to indicate occupancy: of'sections LT and RT.

When the train moves to the right and the rear-of the train vacates section-LT so that the approach relay LAS is reenergized and picked up to open back contact I2, the relay I 2L is deenergized and releases at the end of its slow release period. The relay IL is now picked up over front contacts I9 and 80 during the slow release period of relay IZL, and an impulse of current of normal polarity is supplied to the line circuit, the duration of which impulse is" substantially equaled to the release period of relay I2L. The relay-ID is now picked up and the relay 2P is operated to close its normal polar contact 84 89 in response to this impulse of line circuit current of normal polarity so that the relay 3D is again pickedup, opening back contact interposed in'thestick circuit of relay 4D, with the result that the relay 4D is released, because its slow release period is lessthan the duration of the line circuit current, the duration of the line cire cuit current impulse being determined by the slow release period of relay IZL. It follows that relays 4D and 5D are restored to their normal positions and the lamp LI is extinguished in re'-, sponse to this impulse of current supplied to the line circuit when The relay 6D is not affected by this indication the train vacates the section impulse transmitted as the rear of the train va-v cates section LT. Consequently, the indication relay ID is retained energized over its stick circuit and the lamp RI continues to be displayed to indicate the occupancy of section RT.

When the train proceeds to the right and vacates section RDT so that the approach relay RAS is picked up and the relay IIJL is deenergized, the relay I3L is picked up during the release period of relay IL and a current impulse of reverse polarity is supplied to the line circuit. This impulse of current of reverse polarity operates polar relay 2P 'to close its reverse polar contact 84+96 and relay 6D is picked up. Since the release period of relay ID is less than the release period of relay IIIL, relay ID is released and the lamp RI is extinguished in response'to thisline circuit current impulse of reverse polarity. Thus, it is to be seen that the line circuit current impulse of either polarity is effective to establish a corresponding indication, which indication is continued subsequent to the termination of the current impulse. A second impulse of current of either'polarity is effective to extinguish the indication established in response to the first impulse of current of thecorresponding polarity.

Assuming two trains approach the track switch in Fig. 2, one from the left and the other from the right, and that the train from the left enters section LDT, shunting relay LDTR just a little before the second train enters section RDT, shunting relay RDTR, the approach relay LAS is released and relay ML picked up to cause an impulse of current of normal polarity to be supplied to the line circuit during the slow release period of relay H L, but the approach relay RAS is held energized over its stick circuit including front contact 61 of relay ML until the first impulse is completed. .When relay L is released to terminate the line circuit current impulse caused by the entry of the first train in section LDT, the approach relay RAS is released and the relay l3L is picked up to cause an impulse of current of reverse polarity to be supplied to the line circuit during the slow release period of relay 9L. The current impulse of normal polarity is efiective to cause the indicator Ll to be illuIni-' nated in the manner explained before, and the second impulse is efiective to cause the indicator Rl to be illuminated in the manner explained hereinbefore. Thus, the entry of these two trains in their respective approach sections is indicated at the office station by the apparatus of Fig. 2.

Although I have herein shown and described only two forms of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is: y

1. In combination, a track section having a track relay, an indicator located at an office station for indicating the occupancy of the section, a slow release indication relay for governing said indicator and provided with a pick-up and a. stick circuit, a line circuit extending between the section and the station, oifice station control means for controlling said pick-up and stick circuits and including a winding connected with said line circuit, circuit means governed by said track relay when a train enters the section to supply current to the line circuit to operate said control means to successively close said pick-up and stick circuits, another slow release relay having a slow release period greater than the slow release period of said indication relay and energized when said track relay is released, and a contact of said other slow release relay interposed in said circuit means to at times govern the current supplied to the line circuit for a period suflicient to cause said control means to'open said stick circuit for a period long enough to release said indication relay. I

2. In combination, a track section having a track relay, an indicator located at an ofiice station for indicating the occupancy of the sec tion, a slow release indication relay for governing said indicator and provided with a pick-up and a stick circuit, a line circuit extending between the section and the station, means at the.

office station for controlling said pick-up and stick circuits and including a neutral and a polar? polarity to the line circuit toenergize said neu- I tral and polar relays for closing said indication relay pick-up and stick circuits, a 'slow acting relay having a slow acting period greater than, the slow release period of the indication relay, a contact of said slow acting relay interposed in said circuit means for at times modifying the supply of current tojthe line circuit to operate said neutral relay to open the indication relay stick circuit for a period long enough to release the indication relay, and means governed by said track relay for controlling said slow acting relay.

3. In combination, two sections of railway track, two indicators one for each section located at an ofilce station remote from the sections for indicating the occupancy'of' the sections, two indication relays one for each indicato-n'said re'= lays each having a predetermined slow jrelease period and each operative whenenergi zed to actuate its indicator, a pick-up and astick circuit for each of said relays, a line circuit extendingbetween the'sections and the station, ofiic'e station means for selectively controllingthe pick-up and stick circuits of the indication relaysand including a neutral and a polar relay connected with said line circuit, two control circuit -means one for each section, said circuit means one' operative when a train enters its section to supply current of normal polarity to the linecircuit'for energizing said neutral and polar relaysto close the pick-up and stick circuit of a particular one of the indication relays and the other circuit means operative when a trainent'ers its section to supply current of reverse polarity to theline circuit for energizing said neutral and polar relays to close the pick-up and stick circuits of the other indication relay, two other slowreleasi-ng relays one for each section and each energized when itssection is occupied, said other relays each having a slow release-period greaterfthan said slow release periods of the indicationrelaysf and a contact of eachof said other relays interposed in the circuit means-of the associated sec' tion for causing at times the stick circuit of the corresponding indication relay to be held. open long enough to release the indication relay.

4. In combination, two "sections of railway track, two indicators one for each section located at an ofiice station remote from the sections for indicating the occupancy of the sections, two indication relays one for each indicator, said relays each having a predetermined slow release period and each operative when energized 'to actuate its indicator, a line circuit extending between said sections and said station, polarized control means at the station including a winding connected with said line circuit and operative to energize a particular one of said indication relays in response to line circuit current of normal polarity and to energize the other indication relay in response to line circuit current of. re-

.verse polarity, two circuit means one for each,

station, said circuit means one operative when a train enters its section to supply current of, normal polarity to the line circuit to energize the corresponding indication relay for actuating the associated indicator and the other circuit means operative when a train' enters its section to supply current of reverse polarityto the 11mcircuit to energize the corresponding indication relay for actuating the associated indicator, two other slow release relays one for each section and each energized when its section is occupied, said other relays each having a slow release period greater than said slow release period oftheindication relays, and a contact of each of said other relays interposed in the circuit means of the associated section to govern the line circuit current to release the corresponding. indication relay when a train vacates the associated section.

5. In combination, two sections of railway track, a field station adjacent the sections and a remote ofiice station, a two-wire line circuit extending between said stations, a first circuit means at the field station to continuously supply current of normal polarity to the line circuit when a first one of the sections is occupied, a second circuit means at the field station to continuously supply current of reverse polarity to the line circuit when the second one of the sections is occupied, means controlled by the forward end of a train in passing from either track section into the other section to reverse the polarity of the line circuit current within a predetermined period, slow acting means controlled by the rear end of a train in passing from either section into the other section for holding the line circuit open for a period slightly greater than said predetermined period, and indication means at the ofiice station connected to the line circuit selectively responsive to the polarity of the line circuit current and to said period the line circuit is held open.

6. In combination, two sections of railway track, a field station adjacent the sections and a remote oflice station, a two-wire line circuit extending between the stations,two indicators at the ofiice station one for each section to indicate the occupancy of the section, an indication relay for each indicator operative when energized to actuate its indicator and each of said relays having a predetermined slow release period, a neutral relay and a polar relay at the oifice station connected to the line circuit and operative to selectively energize said indication relays according to the polarity of the line circuit current, a first circuit means at the field station operative when a first one of said sections is occupied to continuously supply current of normal polarity to the line circuit to actuate the indicator of said one section, a second circuit means at the field station operative when the second one of the sections is occupied to continuously supply current of reverse polarity to the line circuit to actuate the indicator for said second section, a stick circuit for each indication relay controlled by said neutral relay whereby either indication relay once picked up by a train in the associated section is retained energized when the train enters the other section and the polarity of the line circuit current is reversed, two slow release relays at the field station one for each section each energized when its section is occupied and each having a slow release period greater than the slow release period of the indication relays, and a contact of each field station slow release relay interposed in the circuit means of the associated section to interrupt the line circuit and release the corresponding indication relay when the train vacates the associated section in passing to the other section.

7. In combination, a track section, a track circuit for the section including a track relay, an

when the train vacates the section, anindication relay at the station having a slowrelease period less than said predetermined period,-av quick acting relay at the station, a pick-up cir-: cuit for the indication relay including a from contact of said quick actingrelay and another contact, a stick circuit for said'indication-relay including a back: contact of said quick acting relay, another relay controlled by said indication relay when picked up to open said other contact, an indication lamp controlled over a frontcontact of said indication relay, and control means at the station including a' winding connected with the line circuit to energize said quick acting relay in response to current flowing 'in said line circuit.

train enters the section and a second similar cur-- rent impulse when the train vacates the section, an indication relay at the ofiice station for controlling said lamp, said indication relay provided with a slow release period slightly less than the duration of said current impulses, and control means at the station connected-with said line circuit operative to pick up said indication relay in response to said first current impulse and to close a stick circuit for the relay at the termination of the current impulse, and said control means operative to open said stick circuit to release said indication relay in response to said second current impulse.

9. In combination, two independent devices each having a first position and a second position, two indicators one .for each device, two slow release indication relays one for each indicator and operative to govern the position of the respective indicator, said relays each provided with a pick-up circuit and a stick circuit, a line circuit, a polarized relay means connected across said line circuit and operative to selectively control the pick-up circuits of said indication relays according to the polarity of the line circuit current, means governed by said polarized means when either indication relay has been energized to close the stick circuit of that indication relay in response to a reversal in the polarity of the line circuit current, circuit means governed by said devices to supply to the line circuit current of normal polarity when a selected one of the devices is operated to its second position and current of reverse polarity when the other device is operated to its second position, two other slow release relays one for each device and each energized at the second position of its device, said other relays each having a slow release period greater than the slow release period of the indication relay for the same device, and a contact of each of said other relays interposed in said circuit means for at times causing the polarized relay means to hold the stick circuit of the corresponding indication relay open long enough to release the indication relay.

10. In combination, a device having a first and a second position, an indicator for indicating the position of the device, an indication relay for governing said indicator, said relay provided with a predetermined slow release period, a line circuit, circuit means controlled by said device to supply to the line circuit an impulse of current' of a selected duration when the device is operated to its first position and to supply a similar impulse of current when the device is operated to its second position, said selected duration of the current impulses made slightly greater than said slow'release period of the indication relay, control means connected to said line circuit and including a quick acting relay which is energized when current flows in the EARL M. ALLEN. 

